1. Field of the Invention
The present invention relates to a photoconductive coat containing specific organic photoconductive compounds and an electrophotosensitive article provided with such a coat.
2. Description of the Prior Art
Electrophotosensitive articles having a photosensitive layer containing inorganic photoconductive compounds such as selenium, zinc oxide, cadmium sulfide and the like as main ingredients have been widely known. However, such known articles are not necessarily satisfactory in terms of thermal stability, durability and other properties and accompanied by manufacturing and handling problems because of toxicity of these compounds.
On the other hand, electrophotosensitive articles having a photosensitive layer containing organic photoconductive compounds as major ingredients have been attracting attention because such articles offer a number of advantages including relative ease of manufacture, relatively low cost, non existence of handling problems and thermal stability that photosensitive elements containing selenium. One of the most popular organic photoconductive compounds for this purpose is poly-N-vinylcarbazole, which is used with Lewis acid of 2,4,7-trinitro-9-freorenon or other substances to form a charge transfer complex material, which is in turn used as a major ingredient of a photosensitive layer of an electrophotosensitive article. Electrophotosensitive articles of this type are already commercially available.
Electrophotosensitive articles having a functionally divided photosensitive layer of either two-layered type or dispersed type, in which the electric charge generation function and the electric charge transfer function are respectively carried by different materials, are also known. For instance, an electrophotosensitive article having a photosensitive layer comprising an electric charge generation layer consisting of a thin film of amorphous selenium and an electric charge transfer layer containing poly-N-vinylcarbazole as a major ingredient is already marketed.
Efforts have been paid to realize an electrophotosensitive article having a functionally divided photosensitive layer as described above by using organic photoconductive compounds for both electric charge generation materials and electric charge transfer materials. Some of the organic compounds that can be used as electric charge generation materials include azo pigments, phthalocyanine pigments, anthraquinone pigments, perylene pigment, cyanine pigment, thiapyrylium pigment and squarium pigment, while some of the organic compounds that can be used for electric charge transfer materials include amine derivatives, oxazol derivatives, triphenylmethane derivatives and hydrazone derivatives.
These electric charge generation and electric charge transfer materials are used with a variety of binding materials to form a film layer as they are not capable of forming a film by themselves. Two types of electrophotosensitive articles are known, a two-layered type having an electric charge generation layer and an electric charge transfer layer formed on an electroconductive support and a dispersed type having a layer containing a certain amount of an electric charge generation material and an electric charge transfer material in a dispersed condition.
However, there are currently few electrophotosensitive articles containing organic photoconductive compounds as electric charge generation materials which are feasible for practical use as they are generally less photoconductive and less durable as compared with those containing inorganic photoconductive compounds.
The object of the present invention is to solve the above mentioned problem by providing a photoconductive coat which is highly sensitive and accompanied by a low residual electric potential and an electrophotosensitive article provided with such a coat which, when used for electric photography in which electric charging, light exposure, development and copy printing processes are repeatedly conducted, exhibits an excellent durability as it is relatively free from deterioration caused by fatigue through repeated use and maintains its original photoconductive characteristics for a long term.